DeJohannes Weiner <hannes@xxxxxxxxxxx> writes: > On Tue, Nov 09, 2010 at 01:24:31AM -0800, Greg Thelen wrote: >> mem_cgroup_page_stat() used to return a negative page count >> value to indicate value. > > Whoops :) > >> mem_cgroup_page_stat() has changed so it never returns >> error so convert the return value to the traditional page >> count type (unsigned long). > > This changelog feels a bit beside the point. > > What's really interesting is that we now don't consider negative sums > to be invalid anymore, but just assume zero! There is a real > semantical change here. Prior to this patch series mem_cgroup_page_stat() returned a negative value (specifically -EINVAL) to indicate that the current task was in the root_cgroup and thus the per-cgroup usage and limit counter were invalid. Callers treated all negative values as an indication of root-cgroup message. Unfortunately there was another way that mem_cgroup_page_stat() could return a negative value even when current was not in the root cgroup. Negative sums were a possibility due to summing of unsynchronized per-cpu counters. These occasional negative sums would fool callers into thinking that the current task was in the root cgroup. Would adding this description to the commit message address your concerns? > That the return type can then be changed to unsigned long is a nice > follow-up cleanup that happens to be folded into this patch. Good point. I can separate the change into two sub-patches: 1. use zero for a min-value (as described above) 2. change return value to unsigned -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>